The premise is made that semantic ambiguity, which is manifested in measuring instruments, could lead to controversial and divergent research results often reported in studies on work motivation. Researchers, the literature indicates, are largely unaware of this phenomenon. In this investigation no studies were found in which semantic ambiguity in questionnaires had been controlled. In order to demonstrate the existence of semantic ambiguity as a phenomenon, a semantic differential was administered to 38 Industrial Psychology students in order to measure the meaning of the items on the Pottas Need Questionnaire. The results indicated that six of the 13 questionnaire items differed significantly from the need categories they purported to measure, which confirmed the notion that semantic ambiguity is a source of variance that should be controlled.